Current Organic Chemistry - Volume 20, Issue 14, 2016

Rare pentoses, especially L-rare pentoses, have been attracting increasing attention because of their medicinal applications in antiviral and anticancer therapy, where they are used to produce L-nucleoside analogues. To address the problems of low natural abundance and limited synthetic methods for rare pentoses, biological synthesis has emerged recently as promising routes to these valuable compounds. This review summarizes enzymatic synthesis and whole cell microbial transformations of seven rare pentoses (L-ribulose, L-ribose, Lxylulose, L-xylose, L-lyxose, D-lyxose, D-xylulose) and two sugar alcohols (xylitol, L-arabinitol) as well as their interconversions. Examples of improving existing enzymes and discovering new systems are also discussed as advancements in genomics and bioengineering.

Sialic acids usually occur as glycosides of functional glycoconjugates such as glycoprooteins and glycolips, that are involved in a wide range of biological phenomena, for example, recognition and adhesion of cellcell, recognition by bacteria and viruses, and tumorigenesis and metastasis. So the synthesis of sialosides is an important field in the design of novel medicines and vaccines. In the last decades, significant efforts for improving stereoselectivity of sialylation have been made. This review summarizes the latest progress in sialylation that can be characterized into several categories: the application of novel leaving group at C-2; combination of leaving group at C-2 with modification of the amino protective groups at the C-5 position; participation of neighboring group at C-1; the influence of O-substituents at C-4 or C-7 on sialylation; some special structure to generate β-sialylation; and using novel promoters and their applications in the synthesis of sialosides.

Disulfide bond plays an important role in various fields, for example, biochemical processes, industrial and pharmaceutical chemistry, bioconjugates, peptidomimetics and selfassembled monolayers (SAMs) etc. In the past decades, drug delivery systems (DDS) have been widely investigated, and disulfide-based oxidation-reduction responsive DDS is the most promising one. Disulfide bonds have no physiological toxicity and remain stable in human body, and can be broken into a reduced form of glutathione (GSH) via the thiol-disulfide exchange reaction. Moreover, the GSH level in tumor tissues has been known to be at least 4-fold higher than that in normal tissues. Therefore, this specific redox potential in cells stimulates people to design oxidation-reduction responsive DDS for specifically releasing drugs in tumor cells and develop the new methods for the preparation of organic disulfanes. The present review has attempted to comprehensively summarize recent advances on the synthetic methods of disulfide bond in drug delivery systems.

Being the first member in the family of nanocarbon superstructures, fullerene C60 (refers to C60 hereafter) continues to be a research focus in physics, chemistry, materials science, biology and life science. The readily available functionalization methods that can be realized on C60 further expand the potential applications of C60 in various fields. Carbohydrates distribute widely in a variety of forms in mammalian animals and the glycan-protein interactions play important roles in many biological processes. Covalently attaching sugar units to C60 yields glycofullerenes, which exhibit interesting physicochemical properties and biological activities. Here, we give a comprehensive review on the syntheses, properties and applications of this novel class of C60 derivatives. Directions in which efforts should be devoted to in near future have also been discussed.

Glyconanoparticles are the subject of numerous literatures and are emerging for applications in biomedicine, glycoscience, and material science due to their unique properties. They are hybrid materials each of which contains a nanoparticle core surrounded by a carbohydrate shell. The core can be metallic, magnetic, and/or photoluminescent, while the shell may be composed of mono-, di-, oligo- and/or poly-saccharides. Sugars are attached to the surface of the nanoparticles through covalent or non-covalent interaction. Here, we give a brief summary of the synthetic methodologies adopted in the preparation of different types of glyconanoparticles, which can be utilized in various applications including catalysis, drug delivery, vaccine, imaging and study of carbohydrate-lectin interactions.

Different synthetic strategies to 4,4-disubstituted pyridazines and condensed pyridazines with a special reference to the synthetic routes to their spiro analogues are comprehensively outlined in this review.